As digital communication techniques advance, various M-ary modulation techniques are developed to be used up to now. In a wired communications field, a baseband type of pulse amplitude modulation (PAM) technique is widely used. PAM-2 can be regarded as a type of a binary code. In addition to PAM-3, PAM-4, and PAM-5, PAM-16 is recently used in that field. Like this, PAM tends to be used for wider applications.
Techniques for generating a modulated carrier wave such as amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK), quadrature amplitude modulation (QAM), etc. are used for wired/wireless modems and satellite communications. In particular, the QAM technique is being used for 4G mobile communications, WiFi, and ultra high definition (UHD) TV transmission, and it is projected to be applied to 5G mobile communications.
In principle, an M-ary modulation technique is a technique for mapping k-bit (k is an integer greater than 0) binary data to M signal components to be transmitted, and, here, M, which is the number of the signal components, is required to be an integer exponent, that is 2k, which restricts the design freedom.
In other words, although more efficient signal transmission is facilitated when M can be freely determined based on the status of a channel on which signals are transmitted, M needs to be selected to satisfy M=2k according to the conventional M-ary signal modulation technique. Thus, a novel M-ary signal modulation technique which facilitates more efficient signal transmission is highly required.